This invention relates to the continuous casting of a lithium-containing alloy such as aluminum-lithium alloy.
Conventionally, large ingots of high strength light metal, e.g., such as aluminum, are produced by continuous direct chill casting of molten metal using water as the direct chill coolant. A continuous ingot having a solid surface but a core which is still molten is formed in a water-cooled mold. After passing through the mold, coolant impinges directly on the hot solid ingot surface to provide direct chill cooling. The water then separates and falls from the ingot after extracting heat.
Lithium-containing alloys, such as aluminum-lithium alloys, offer substantial advantages for high technology applications such as aircraft plate, sheet, forgings, and extrusions. Light metal lithium-containing alloys are highly regarded for material properties such as low density, high strength, high modulus of elasticity, and high fracture toughness. The combination of these material properties can reduce the weight of large commercial airliners by as much as six tons or more. The resulting weight savings can reduce an aircraft's fuel consumption by 220,000 gallons or more during a typical year of operation.
A process for continuously casting lithium-containing alloys into acceptable ingots of large size depends on the manner of cooling. Typically, water is used as the direct chill coolant in conventional processes. However, water coming into contact with lithium-containing alloy has been found to present a substantial risk of violent explosion. This risk can be minimized or eliminated through the use of an inventive continuous casting process as described in related U.S. patent application Ser. No. 550,466, filed Nov. 10, 1983.
However, a further problem has been discovered in the continuous casting of lithium-containing alloy which stands in the way of the substantial commercial development of large-scale applications such as large size ingot for aircraft plate and sheet.